1. Field of the Invention
The present invention relates to a position detector, a position detection method, an exposure apparatus, and a device manufacturing method.
2. Description of the Related Art
A prior art of a position detector in a semiconductor manufacturing exposure apparatus shown in FIG. 9 will be described.
First of all, a wafer stage 12 is moved to a position where a mark WM on a wafer W can be observed. A pattern (registered pattern) of the mark WM is illuminated with a light beam applied from a mark illumination system 2, which applies non-exposure light, via an imaging optical system 4 and a beam splitter 3. In FIG. 2, a shows an example of the registered pattern. A light beam reflected by the registered pattern reaches the beam splitter 3 again. The light beam is reflected by the beam splitter 3 to form an image of the registered pattern on the image sensing surface of an image sensing unit 6 via an imaging optical system 5. The image sensing unit 6 photoelectrically converts the image of the registered pattern. An A/D conversion unit 7 converts the image of the registered pattern into a two-dimensional digital signal string. An edge position extraction unit 8 differentiates the two-dimensional digital signal string in the x and y directions and extracts coordinates having high differential values like the crosses in b of FIG. 2, as candidate points of template feature points. A template feature point creating unit 9 selects spatially uniformly distributed template feature points like those shown in c of FIG. 2 from the extracted candidate points. The selected template feature points are stored in a template storage unit 10, and are called by a matching unit 11 to be used for template matching processing at the time of measurement of a mark position.
The above conventional position detector is effective for an apparatus which detects template feature points from a registered pattern, registers them, and performs matching processing for the registered template to measure an alignment mark. However, various patterns other than a registered pattern may exist on the wafer W, and some of them may resemble the registered pattern. If the shape of a mark to be detected is known in advance, as disclosed in Japanese Patent Laid-Open No. 2003-338455, a template which prevents erroneous detection of a similar pattern can be also created in consideration of non-edge portions of the mark. Even if template feature points are determined by the conventional position detector, there is a possibility that a pattern other than the mark to be detected will be detected.